01 - Preheat oven to 350°F. Pat duck dry with paper towels. Prick skin all over carefully without piercing the meat.
02 - Season cavity and skin with salt and black pepper. Stuff cavity with quartered orange, onion, and thyme sprigs.
03 - Place duck breast-side up on a rack in a roasting pan. Roast for 1 hour, draining excess fat every 30 minutes.
04 - In a small saucepan, combine orange juice, zest, honey, soy sauce, ginger, garlic, vinegar, and chili flakes if used. Simmer over medium heat, stirring occasionally, until syrupy, about 10–12 minutes. Set aside.
05 - Brush duck all over with glaze after 1 hour. Return to oven and roast 30–40 minutes more, glazing every 10–15 minutes, until skin is deep golden and crispy and internal temperature reaches 165°F.
06 - Remove duck from oven. Loosely cover with foil and rest for 15 minutes before carving. Serve with remaining glaze.